I just installed the GM version of Mavericks and, as a constant bitcher of 10.8.4/5, well, this is, indeed, a breath of fresh air. First of all, I'm running 10.9 on a secondary firewire/800 connected disk on a 2008 MBP with 6 Gb of RAM and a 2.6 Ghz duo core processor. My initial observations: 1. Install took 45 minutes but was flawless. 2. Faster in almost every interaction between me and this 5 year old computer. I am coming from being totally pissed with 10.8.x so I have to admit I was a skeptic. 3. The integration between my MBP and my iDevices is really cool: maps, calendars, contacts etc. 4. And now iBooks works on a Mac. This was one of those ...WTF was Apple thinking by not including this in 10.8...or 10.7 for that matter. I can buy they book in iTunes but I can READ it on the device I ordered it on? Wow! 5. Memory management and power management is VASTLY improved, just as promised. For road warriors, this is a huge selling point all by themselves. 6. Oh, yeah, and the multiple display features are very cool! The net-net for me: Stability and performance improvements are worth the upgrade. I can only imaging how well this will run on a more contemporary machine. This is an evolutionary upgrade, not revolutionary. And that's OK by me.